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Rebecca J. McLean, Irene Gottlob, Frank A. Proudlock; Are Eye Movement Recordings Or Visual Acuity The Better Outcome Measure For Nystagmus: A Test-retest Analysis. Invest. Ophthalmol. Vis. Sci. 2012;53(14):510.
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With the recent emergence of therapeutic clinical trials for nystagmus, the issue of the most appropriate and sensitive outcome measures has been the subject of debate. In this study test-retest analysis has been assessed on the common outcome measures of visual acuity (VA) and eye movement recordings (EMR) in order to assess their reliability.
Forty volunteers with infantile nystagmus syndrome (INS) (27 idiopathic, 13 albinism) were assessed by one investigator, on two separate occasions, 5-8 weeks apart. Best-corrected logMAR visual acuity (BCVA) was recorded at distance (1.2m) and near (0.4m) and gaze-dependant visual acuity (GDVA), -30° to +30° in 5° steps, at distance. EMR (500Hz) along the horizontal meridian (-30° to +30° in 3° steps) were used to derive amplitude, frequency, intensity and foveation (NAFX) measured at distance and near. Intra-class correlation coefficient (ICC) was applied to measure the strength of agreement between repeated measures. Levene’s test was used to test for significant differences in variance between test-retest differences.
VA and EMR outcome measures averaged from -30° to +30° demonstrated high reliability for both distance viewing (ICC 0.96 for BCVA (95% CI: 0.93-0.98) and 0.97 for GDVA (95% CI: 0.95-0.99); ICC >0.93 for all eye movement outcome measures) and near viewing (ICC 0.90 for BCVA (95% CI: 0.82-0.95); ICC 0.70 to 0.83 for all eye movement outcome measures). However, test-retest differences showed significantly higher variances for near viewing compared to distance viewing (p=0.017 for BCVA and p<0.05 for all EMR). Higher variances in test-retest difference were also observed for EMR outcome measures recorded at the null region (ICC was 0.74 to 0.94 for distance; 0.66 to 0.86 for near) compared to the average of all positions (-30° to +30°), and also for INS associated with albinism (mean ICC = 0.76) compared to idiopathic INS (mean ICC = 0.80).
We have shown for the first time that parameters currently used in clinical trials to assess nystagmus are reliable. Parameters with highest strength of agreement between measurements are distance viewing for BCVA and all EMR parameters when averaged across the horizontal plane. BCVA and eye movement measures at near viewing were less consistent. Establishing reliable outcome measures for nystagmus will provide standardised parameters that can be performed across nystagmus studies.
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